1. Field of the Invention
The present invention relates to a toner used in image forming methods such as electrophotography, electrostatic recording, electrostatic printing, and toner-jetting recording system.
2. Description of the Related Art
Many proposals have been made with respect to a technique for improving the developing performance and durability of a toner, by controlling an affinity of the toner to a particular solvent. Examples of such technique include a technique in which a toner is dispersed into a mixed solvent of ethanol and water to measure the absorbance at the time, thereby finding an amount of magnetic iron oxides that exist on the surface of magnetic toner. With this technique, the extent of contamination a charging roller caused by the magnetic toner and the extent of the magnetic toners sticking to a photosensitive drum can be easily known (refer to JP11-194533A, for example).
Another example of such technique is a technique related to a toner having a predetermined wettability with respect to ethanol. In this technique, the hydrophobic property of the toner is expressed on the ethanol dropping transmittance curve, and the transmittance against the ethanol content by percentage is measured (refer to JP 2000-242027A, for example).
In addition to the given examples, there is a technique with which a charging property of a toner is improved by relating a surface condition of the magnetic toner with an absorbance of the magnetic toner dispersed in a methanol and water mixed solvent at the time (refer to EP1241530A1, for example).
Nevertheless, it is difficult to overcome all of the problems associated with recent increase in operation speed of electrophotographic devices such as problems which happen in and around a fixing device, end-offsetting, and a decline in the image density that is caused by charge-rise phenomenon of the toner.
Regarding to the polyester resin, which is used in toners, a tetrahydrofuran (THF) insoluble matter is 5% by mass or less, and in a THF soluble matter, proportions of ultra high molecular weight matter of 1×106 or more, high molecular weight matter of 1×105 or more, low molecular weight matter of less than 1×104, and middle molecular weight matter of 1×104 or more and less than 1×105 are defined (refer to JP10-60104A and JP10-69126A, for example).
However, it is difficult to solve the problem of end-offset by only defining proportions of the various molecular weight cutoff of polyester resin.
In addition, the polyester resin for toner, wherein the polyester resin has a maximum of molecular weight in the range of 1×103 to 8×103, has a Mw/Mn ratio value in the range of 20 to 200; has no more than 80% by mass, to the whole resin, of a component of molecular weight 1×105 or less; and the polyester resin comprises polycarboxylic acid with 3 or more carboxyl groups and/or polyhydric alcohol with 3 or more hydroxyl groups; is known as polyester resin for electrophotographic toner (refer to JP 9-251216A, for example).
As disclosed in this publication, a toner having a wide non-offset temperature range is obtainable. However, charge control of the toner is insufficient such that the toner has a difficulty in complying with high speed.
In addition, a toner comprising polyester resin using oxyalkylene ether of novolak type phenolic resin is known as a toner comprising polyester resin (refer to JP 9-251217A and JP 11-24312A, for example).
However, the characteristic of the polyester resin is that it does not comprise tetrahydrofuran (THF) insoluble matter. Thus, this toner has difficulties in satisfying the high temperature offset property and developing performance in a higher level.
In addition, as a polyester resin for use a toner binder, there is a polyester resin for a toner binder that uses oxyalkylene ether of novolak type phenolic-resin (refer to JP 5-27478A, for example) is known. In addition, in regard to a toner, a toner which comprises a resin that comprises polycarboxylic acid component and polyol component, in which at least one part of the polyol component is oxyalkylene ether of novolak type phenolic resin with 3 or more hydroxyl groups, and a THF insoluble matter of 0.1 to 20% by mass (refer to JP 2000-242030A, for example) is known.
According to these inventions, the problems of high temperature offset property and fixing property are definitely improved. However, there is still a room for further improvement since a hydrophobicity of the toner is not yet controlled, and a property of the toner is still greatly influenced by an environment.